1. Technical Field
The present invention relates in general to data storage and processing and, in particular to virtual storage systems. More particularly, the present invention relates to a method and system for efficiently importing/exporting removable storage volumes between virtual storage systems.
2. Description of the Related Art
In hierarchical virtual storage systems, intensively used and frequently accessed data is stored in fast but expensive memory. One example of a fast memory is a direct access storage device (DASD). In contrast, less frequently accessed data is stored in less expensive but slower memory. Examples of slower memory are tape drives and disk drive arrays. The goal of the hierarchy is to obtain moderately priced, high-capacity storage while maintaining high-speed access to the stored information.
One such hierarchical storage system is a virtual tape storage system (VTS), including a host data interface, a DASD, and a number of tape devices. When the host writes a logical volume, or a file, to the VTS, the data is stored as a file on the DASD. Although the DASD provides quick access to his data, it will eventually reach full capacity and a backup or secondary storage system will be needed. An IBM 3590 tape cartridge is one example of a tape device that could be used as a backup or secondary storage system
When the DASD fills to a predetermined threshold, the logical volume data for a selected logical volume is then appended onto a tape cartridge, or a physical volume, with the original left on the DASD for possible cache hits. When a DASD file has been appended to a tape cartridge and the original remains on the DASD, the file is xe2x80x9cpremigrated.xe2x80x9d
When the host reads a logical volume from the VTS, a cache hit occurs if the logical volume currently resides on the DASD. If the logical volume is not on the DASD, the storage manager determines which of the physical tape volumes contains the logical volume. The corresponding physical volume is then mounted on one of the tape devices, and the data for the logical volume is transferred back to the DASD from the tape.
Typically, a database containing information that links the logical volumes to their corresponding physical tape volume is maintained by the VTS. Generally, the database is maintained and backed up separately from the data tapes. This database, however, does not store the actual logical volume name, instead it utilizes a reference number for the logical volume name. This makes it difficult to quickly import and export to and from a VTS because all the data files must be typically be read by the receiving VTS, in the case of an import operation, to generate the information that links the logical volumes to their corresponding physical data tape for the receiving VTS database.
Accordingly, what is needed in the art is an improved method for importing/exporting data tapes from one VTS to another VTS that mitigates the above-discussed limitations in the prior art. More particularly, what is needed in the art is an improved method for importing/exporting data tapes that does not require the receiving VTS to read every data file in the imported data tapes to generate the information that links the logical volumes to their corresponding physical tape volume.
It is therefore an object of the invention to provide an improved virtual storage system.
It is another object of the invention to provide a method and system for efficiently importing/exporting removable storage volumes between virtual storage systems.
To achieve the foregoing objects, and in accordance with the invention as embodied and broadly described herein a method and system for efficiently importing/exporting a removable storage volume having a number of data files from a first virtual storage system to a second virtual storage system is disclosed. The method includes writing a table of contents to the end of the removable storage volume in the first virtual storage system. The table of contents uniquely identifies the data files residing in the removable storage volume. Next, the removable storage volume is transferred to the second virtual storage system. Upon receipt of the removable storage volume, the second virtual storage system updates a database in the second virtual storage system utilizing the information contained in the table of contents without having to read each of the data files. In a related embodiment, for each of the data file in the removable storage volume, the table of contents includes a filename, starting record on the removable storage volume and number of records in the data file and the table of contents is written to the end of the removable storage volume when the removable storage volume is closed. In another advantageous embodiment, the table of contents further includes a timestamp that provides a means of determining when the data files were written to the removable storage volume.
In another embodiment of the present invention, the table of contents is written to the end of the removable storage volume after the removable storage volume has been idle for a period of time. This has the added advantage that if an intervening system crash occurs before the removable storage volume is filled, the table of contents in the partially filled removable storage volume can be utilized to restore a database that contains the information detailing the links between the logical and physical volumes.
The foregoing description has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject matter of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.